Comment 19 for bug 1636847

@SaveTheRbtz I did get to the cause, and added a lot of notes about it in the comments for this bug. I even wrote some code to provide a more balanced compromise between memory usage and performance, but once the memory issues were alleviated it seems no one cared about it enough to even try out the test kernels.

I don't know if things have improved upstream with the ram usage of CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU. It's probably worth a look. On most systems with a small number of possible cpus and a small number of squashfs mounts it no doubt works fine, but the introduction of snaps caused a big increase in the number of squashfs mounts in Ubuntu systems, which makes CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU problematic if it still has the same behavior.